156 Mr Kenwood on the Phenomena of 



part altogether disappears, or is only continued in minute 

 strings ; in this case the lode is said to have dwindled away, or 

 to have been wj'ung out. It also frequently happens that both 

 these principal parts (the rock and the quartz) are intimately 

 united, producing a siliceous layer of rock, which is still metal- 

 liferous, and is commonly called the capel; hence the courses 

 of schorl-rock, porphyry, and some anomalous rocks, which 

 have been called by the miners elvans, have been properly 

 considered by them to be analogous to lodes, for they are in 

 fact veins on a larger scale. 



"It has been already stated that the elvans pass by gradual 

 transitions into the adjoining rocks ; and it may be mentioned, 

 that the same intimate connection which subsists between the 

 quartzose part of veins and the included portions of slate 

 (horses of killas) also obtains between the veins and the main 

 rock. I have invariably found that this phenomenon is com- 

 mon to the metalliferous veins of Cornwall. This fact appears 

 to explain why the matrix of lodes bears a relation to the con- 

 taining rock ; and why the metallic contents of lodes, in like 

 manner, vary both in their nature and quantity. 



From the same authority, in his valuable " Treatise on Pri- 

 mary Geology," we learn that large metalliferous veins, like 

 the lesser ones, which are confined to rock concretions, though 

 they may sometimes appear to have walls or way-boards, yet 

 these are not essentially necessary, being often only found in 

 certain parts of the veins, and may therefore be attributed to 

 accidental circumstances, such as the peculiar manner in which 

 the substance of the lode was aggregated ; the occurrence of a 

 smaller vein of a different mineral, parallel and sometimes co- 

 incident to the sides of the larger, but far more frequently to 

 the subsequent formation of seams or fissures, by the alternation 

 of the rock at the junction of the veins resulting from decom- 

 position, the effects of the percolation of water, or of the action 

 of the elements. How can we otherwise account for the fact, 

 that many parts of those veins, exhibiting what have been call- 

 ed regular walls, are intimately connected with the adjacent 

 rock, not only as it were by a mechanical union, but often by 

 a transition of mineral composition, so that in granite the union 

 is generally effected by the rock becoming gradually more and 



